The present invention generally relates to a railroad car energy absorption apparatus and, more particularly, to a railroad car energy absorption apparatus including a spring assembly having an elastomer spring element arranged in operable combination with structure for inhibiting localized heat deterioration of the elastomer spring element.
An energy absorption apparatus is known to be utilized on a railroad car in various applications and between two masses. For example, an energy absorption apparatus is typically arranged in operable combination with a railroad car draft gear for absorbing forces between adjacent ends of railroad cars. A railroad car energy absorption apparatus is also commonly configured as a side bearing. A railroad car side bearing is typically disposed to opposite sides of a car body between a centerpiece or bolster of a wheeled truck and an underside of the railroad car body. During movement of the railcar, each side bearing acts as an energy absorption apparatus and furthermore serves to control or restrict xe2x80x9chuntingxe2x80x9d movements of the railcar.
Hunting is a phenomenon created by the wheeled trucks during movement of the railway vehicle over tracks or rails. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they continually seek a centered position under the steering influence of wheel conicity. In traveling such a sinuous path, a truck will yaw cyclically in an unstable fashion with respect to the car body about an axis defined by a vertical centerline of the truck bolster. Hunting, and the resulting side or lateral translation or oscillation of the railway car body is of particular significance when the car is traveling in an empty condition at relatively high speeds, e.g., in excess of 45 miles per hour. Of course, the truck also tends to yaw or rotate quasi-statically with respect to the car body in negotiating curved sections of track. Suffice it to say, excessive hunting can result in premature wear of the wheeled truck components including the wheels. Hunting can also cause damage to lading being transported in the railroad car body.
Known railroad car energy absorption devices typically use compressed resilient members such as spring loaded steel elements or elastomeric blocks or columns or both. The spring loaded steel elements, utilizing a steel on steel friction interface, proved ineffective in some applications because of seizing and galling problems. Recently different forms of thermoplastic elastomers have advantageously been used to develop the necessary force absorption characteristics required for such railroad car uses. One such elastomer is marketed and sold by the Assignee of the present invention under the tradename xe2x80x9cTecsPakxe2x80x9d.
Regardless of the application, the buildup of heat in proximity to the thermoplastic spring is a serious concern. During operation of the railroad car and use of such energy absorption apparatus, heat develops. Unless such heat buildup can be controlled, however, the thermoplastic spring will tend to soften and deform, thus, adversely affecting the operable performance of the railroad component with which it finds utility. For example, as a wheeled truck yaws back and forth, an undersurface of the railcar body slides across and relative to a metal top plate of the side bearing which is biased against the undersurface of the railcar body by the elastomeric spring. The resulting friction advantageously produces an opposite torque which acts to inhibit yaw motion. Such resulting friction also typically causes an excessive amount of heat at the interface between the top plate and the underside of the car body. Such heat buildup often exceeds the heat deflection temperature of the thermoplastic spring. As used herein and throughout, the term xe2x80x9cheat deflection temperaturexe2x80x9d means and refers to a temperature level at which the related component, regardless of its composition, tends to soften and deform.
When such localized heat created by the friction between the side bearing and the car body exceeds its heat deflection temperature, the elastomeric spring will tend to deform and/or, when the temperature is high enough, cause melting of the elastomeric spring. Deformation and melting of the elastomeric spring significantly reduces the ability of the spring to apply a proper preload force and, thus, decreases vertical suspension characteristics of the side bearing which, in turn, results in enhanced hunting of the wheeled truck. Enhanced hunting and/or unstable cyclic yawing of the truck increases the resultant lateral translation/oscillation of the railcar leading to a further increase in the levels of heat buildup and further deterioration of the elastomeric spring.
Thus, there is a need and continuing desire for a railroad car energy absorption apparatus having a spring assembly including an elastomeric spring arranged in operable combination with structure for inhibiting deterioration of the elastomeric spring resulting from localized heat.
In view of the above, there is provided a railroad car energy absorption apparatus which is specifically designed to limit the adverse affects local heat has on such apparatus. In accordance with one aspect of the invention, a railroad car side bearing assembly is adapted to be disposed intermediate an elongated bolster and a car body of a railway vehicle. The side bearing includes a housing and a cap or top plate which is movable toward and away from the housing. Both the housing and cap include wall structure which, when the cap is arranged in operable combination with the housing, combine to define a cavity or void in the side bearing. An elastomeric spring is accommodated within the cavity between the housing and cap for urging the surface on the cap against the bottom of the car body. According to one aspect of the present invention, the housing wall structure and the cap wall structure are each configured to promote dissipation of heat away from the elastomeric spring thereby prolonging effective usefulness of the side bearing assembly.
The elastomeric spring is preferably formed from a thermoplastic elastomer capable of imparting a predetermined preload or force to the cap or plate of the side bearing assembly to inhibit hunting movements of the wheeled truck as the railroad car moves along the tracks. In a preferred embodiment, the elastomeric spring defines a generally centralized throughbore which opens at opposite ends in the direction of spring compression.
Preferably, the housing wall structure and the cap wall structure are each configured to limit generally horizontal shifting movements of the cap relative to a longitudinal axis of the housing. Moreover, the housing and cap are each configured to allow movement of the cap relative the housing while inhibiting rotation therebetween.
In a preferred embodiment, the housing wall structure has a noncomplete configuration toward a free end thereof In one form, the housing wall structure comprises only between about 30% and about 70% of a free end boundary of the housing wall structure. More specifically, the housing wall structure preferably defines openings arranged to opposed lateral sides of a longitudinal axis of the side bearing and which generally align with openings in the cap wall structure to permit air to move into the side bearing, around the elastomeric spring, and, ultimately, from the cavity whereby venting heat away from the elastomeric spring thereby prolonging usefulness of the side bearing assembly.
Preferably, the openings defined by the cap wall structure extend away from a planar surface of the cap and toward a free end of the cap wall structure for a distance measuring between about 35% and about 60% of a distance measured between the planar surface of the cap and the free end wall structure of the cap. Moreover, in a preferred embodiment, the planar car body engaging surface of the cap is configured to promote both free and forced convection of heat from the cavity wherein the elastomeric spring is operably disposed.
In that embodiment wherein the elastomeric spring has a centralized throughbore, at least one of the housing and the cap is provided with a guide to positively position the elastomeric spring relative to the other side bearing components. Additionally, at least one of the cap and housing has a stop for limiting movement of the cap toward the housing and thereby controlling spring compression during operation of the railroad car side bearing.
In accordance with another aspect, there is provided a spring assembly including an elastomeric spring whose elongated axis defines a longitudinal axis of said spring assembly and which has a thermal insulator or air spacer arranged in operable combination therewith to restrict conductive heat transfer to the spring. The thermal insulator defines one end of the spring assembly and is configured to direct air to move across the thermal insulator in a direction generally normal to the longitudinal axis of the spring thereby promoting convective heat transfer away from the elastomeric spring whereby prolonging usefulness of said spring assembly.
As will be appreciated from an understanding of this disclosure, the principals inherent with providing a thermal insulator in combination with a railroad car spring assembly are equally applicable to substantially any shape or design of thermoplastic spring arranged in combination therewith. In a preferred embodiment, the thermoplastic elastomer spring has a generally cylindrical-like configuration between opposed ends. Preferably, the elastomeric spring defines an open ended recess arranged adjacent to the thermal insulator.
In a most preferred form, the elastomeric spring has a generally centralized bore opening at opposite ends of the elastomeric spring. Moreover, in a preferred form, the thermal insulator is likewise provided with a generally centralized throughbore open at opposite ends.
The thermal insulator is preferably formed from a nylon or other suitable thermoplastic material having a relatively high impact strength and low thermal conductivity. Suffice it to say, the material used to form the thermal insulator has a heat deflection temperature which is significantly greater than a heat deflection temperature of the elastomer used to form the elastomeric spring. In a preferred embodiment, the thermal insulator generally comprises about ⅕ to about {fraction (1/20)} of the distance between opposed ends of the spring assembly. In one form, the thermal insulator includes spaced and generally parallel surfaces defining a distance of about 0.250 inches and about 1.0 inch therebetween.
The thermal insulator is preferably provided with structure for operably securing the insulator to the elastomeric spring. To facilitate assembly of the spring, and to further ensure appropriate matching of the spring assembly with the railroad car component with which it is intended to find utility, the thermal insulator is preferably color coded to visually indicate certain characteristics of the elastomeric spring arranged in operable combination therewith.
In one form, a free end of the thermal insulator includes a series of buttons or lugs arranged in a uniform pattern relative to each other such that opposed sides of adjacent buttons defining a passage therebetween. The passages defined between adjacent buttons extend across the thermal insulator in generally normal relation relative to the longitudinal axis of the spring assembly. Preferably, a free end of the series of buttons combine to define a generally planar surface, and with the free end of the buttons collectively comprising between about 30% and about 75% of the total surface area of one end of the spring assembly. In one embodiment, the buttons generally comprise about xe2x85x9c to about xc2xe of a distance between generally parallel surfaces on the thermal insulator. Alternatively, the series of buttons or lugs project from and are operably associated with a metal plate to promote transfer of heat from the elastomeric spring.
According to another aspect, the apparatus for absorbing energy includes a housing adapted to be arranged in operable combination with one of two masses. Such apparatus further includes a member mounted in movable and generally coaxial relation relative to the housing. Such member defines a surface adapted to be arranged in operable relation with the other of two masses. Such apparatus furthermore includes a spring assembly adapted to be disposed between the housing and member for absorbing energy imparted to said apparatus by either or both of said first or said second masses. The spring assembly includes an elastomeric spring and a thermal insulator defining that end of the spring assembly adapted to be disposed adjacent the member, and wherein the thermal insulator is adapted to restrict conductive heat transfer from such member to the elastomeric spring. Furthermore, the thermal insulator is configured to direct air across an interface between the thermal insulator and the member thereby promoting convective heat transfer from that end of the elastomeric spring arranged adjacent the member so as to prolong usefulness of the spring assembly.
According to still another aspect of the present invention, there is provided an elastomeric spring assembly including an elongated thermoplastic spring having first and second axially spaced ends and an encapsulator arranged relative to the first end of the spring. As will be appreciated, certain elastomers tend to deform as a result of repeated heat cycling applied to a localized area of the thermoplastic spring and at temperatures of about 250xc2x0 F. As such, the purpose of the encapsulator is to inhibit deterioration and radial deflection of the first end of the spring as a result of repeated heat cycling applied to the thermoplastic spring.
In a preferred form, the encapsulator includes a closed band extending about and axially along a lengthwise distance of the thermoplastic spring. As will be appreciated by those skilled in the art, the axial distance the closed band extends along an outer surface of the elastomeric spring in minimized to maximize the operational characteristics of the elastomer spring while allowing the band to remain effective to achieve the intended purpose.
According to yet another aspect, there is provided a spring assembly including an elastomeric spring having predetermined load-deflection characteristics and disposed between two masses. The spring assembly further includes an encapsulator for inhibiting the associated local portion of elastomeric spring from deforming after exposure to heat deflection temperatures which would normally cause spring performance deformation or deterioration whereby assisting the elastomeric spring to maintain its predetermined load-deflection characteristics.
When the apparatus for absorbing energy is designed as a railroad car side bearing, the closed band on the spring assembly is arranged toward that end of the spring adapted to be exposed to increased heat levels which commonly result during operation of the railroad car side bearing. As such, the closed band inhibits that end of the spring exposed to heat from deforming as a result of xe2x80x9chuntingxe2x80x9d movements of the wheeled trucks on the railroad car.
When the energy absorption apparatus is configured as a railroad car side bearing, and to further address concerns regarding heat deterioration of the elastomeric spring, besides having one end of the spring surrounded by a closed band, the housing and cap of the side bearing are preferably configured as described above to allow heat to enter the cavity wherein the elastomeric spring is disposed, circulate about the spring, and, ultimately, pass from the side bearing to dissipate heat buildup and, thus, prolong useful life of the railroad car side bearing.
Accordingly, one object of this invention is to provide a railroad car energy absorption apparatus which is designed to limit the adverse affects localized heat has on such apparatus.
Another object of this invention is to provide an elastomeric spring assembly including an elastomeric spring including structure for inhibiting deterioration of the spring as a result of heat.
Still another object of this invention is to provide an elastomeric spring assembly which is designed to provide predeterminable load characteristics and which is structured to maintain the configuration of the spring so as to consistently provide such predeterminable load characteristics notwithstanding the operational heat applied thereto during operation of the spring assembly.
Another purpose of the is invention is to provide an elastomeric spring assembly which is designed to limit physical deformation of the elastomeric spring notwithstanding repeated exposure to heat deflection temperatures which would normally cause heat deformation of the elastomeric spring.
Still another object of this invention is to provide an apparatus including an elastomeric spring adapted to absorb and return energy between two masses and wherein a thermal insulator is arranged in operable combination with and is intended to restrict heat transfer to one end of the elastomeric spring by directing air across an interface between the thermal insulator and that movable mass with which the apparatus is in contact thereby promoting conductive heat transfer from that end of the elastomeric spring arranged proximate to the movable mass.
Yet another object of this invention is to provide a railroad car side bearing which includes an elastomeric spring for resiliently urging a cap against and into sliding contact with an undersurface of a railway vehicle and wherein wall structures on a housing and cap of the side bearing are configured relative to each other to promote convection of heat away from the elastomeric spring thereby prolonging usefulness of the railroad car side bearing.
Still a further purpose of this invention is to design a railroad car side bearing such that an elastomeric spring arranged in combination therewith is protected against heat damage resulting from hunting movements of a wheeled truck on which the side bearing is mounted.
Another purpose of this invention is to produce an economical and cost efficient railroad car side bearing utilizing an elastomeric spring which is protected against heat damage resulting from hunting movements of a wheeled truck on which the side bearing is mounted.
These and other objects, aims, and advantages of the present invention are more fully described in the following detailed description, the appended claims, and drawings.